Antagonistic potential and phylogeny of culturable endophytic fungi isolated from desi cotton (Gossypium arboreum L.)

Twenty three fungal endophytes isolated from desi cotton (Gossypium arboreum) were evaluated against two important pathogens of cotton Corynespora cassiicola and Fusarium solani, causal agents of leaf spot and seedling rot respectively. The internal transcribed spacer (ITS) region analysis was used for species-level identification of the fungal endophytes, wherein Curvularia (11) genus followed by Nigrospora (4) was found dominant whereas, Alternaria sp. (2) and Setosphaeria rostrata (2) were other prominent endophytes. Two isolates of Nigrospora sphaerica (CEL 5 and CEL 19) were highly efficient against C. cassiicola and inhibited mycelial growth up to 49.38% and 46.30%, respectively, whereas another isolate of N. oryzae (CEL 2) was effective against F. solani with inhibition of 43.06%. Besides, N. sphaerica (CEL 19) was found to influence the growth of test pathogens when tested for antibiosis. Through GC/ MS analysis of CEL 19 isolate, four major antimicrobial volatile organic compounds (VOCs), namely 1, 3‑diethyl benzene, 1, 4-diehtyl benzene, m-Ethylacetophenone, and p-cymene-7-ol were identified. The phylogeny tree constructed based on ITS sequences revealed two major branches and the first major branch consisted of most of the isolated fungal endophytes, whereas the second major branch consisted of only Coprinopsis cinerea and Puccinia chunjii. The 23 isolates divided into Ascomycota and Basidiomycota phyla were represented by four classes; Agaricomycetes, Eurotiomycetes, Sordariomycetes and Dothidiomycetes which were distributed into six orders. The majority of endophytes belonged to class Dothidiomycetes, followed by Sordariomycetes. There was no much difference observed between the endophytes and the reference taxa, even though it was a pathogen, indicating that pathogenicity of an organism is always not correlated with its gene sequence. Our findings suggest that N. sphaerica could be used as a potential biocontrol agent and its VOCs also have a role in suppressing the growth of plant pathogens.